• Journal of Electrochemical Science and Technology
• /
• v.2 no.1
• /
• pp.39-44
• /
• 2011

Sub-micrometer $La_{0.8}Ca_{0.2}CrO_3$ powders for ceramic interconnects of solid oxide fuel cells were synthesized by the aqueous combustion process. The materials were prepared from the precursor solutions with different glycine (fuel)-to-nitrate (oxidant) ratios (${\phi}$). Single-phase $La_{0.8}Ca_{0.2}CrO_3$ powders with a perovskite structure were obtained after combustion when ${\phi}$ was equal to or larger than 0.480. Especially, the stoichiometric precursor with ${\phi}$ = 0.555 yielded the spherical $La_{0.8}Ca_{0.2}CrO_3$ particles with 150-250 nm diameters after calcination at $1000^{\circ}C$. When compared with the powders synthesized by the solid-state reaction, the combustion-derived, fine powders exhibited improved sinterability, leading to near-full densification at $1400^{\circ}C$ in oxidizing atmospheres. Moreover, a small quantity of glass additives was used to reduce the sintering temperature, and considerable densification was indeed achieved at temperatures as low as $1100^{\circ}C$.

• International Journal of Oral Biology
• /
• v.46 no.3
• /
• pp.105-110
• /
• 2021

The physicochemical properties of crystalline titanium dioxide nanoparticles (TiO₂ NPs) were investigated by comparing amorphous (amTiO₂), anatase (aTiO₂), metaphase of anatase-rutile (arTiO₂), and rutile (rTiO₂) NPs, which were prepared at various calcination temperatures (100℃, 400℃, 600℃, and 900℃). X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed that the phase-transformed TiO₂ had the characteristic features of crystallinity and average size. The surface chemical properties of the crystalline phases were different in the spectral analysis. As anatase transformed to the rutile phase, the band of the hydroxyl group at 3,600-3,100 cm^-1 decreased gradually, as assessed using Fourier transform infrared spectroscopy (FT-IR). For ultraviolet-visible (UV-Vis) spectra, the maximum absorbance of anatase TiO₂ NPs at 309 nm was blue-shifted to 290 nm at the rutile phase with reduced absorbance. Under the electric field of capillary electrophoresis (CE), TiO₂ NPs in anatase migrated and detected as a broaden peak, whereas the rutile NPs did not. In addition, anatase showed the highest photocatalytic activity in an UV-irradiated dye degradation assay in the following order: aTiO₂ > arTiO₂ > rTiO₂. Overall, the phases of TiO₂ NPs showed characteristic physicochemical properties regarding size, surface chemical properties, UV absorbance, CE migration, and photocatalytic activity.

• New & Renewable Energy
• /
• v.18 no.2
• /
• pp.40-49
• /
• 2022

In this study, the phase and electrochemical properties of Co and Ti substituted layered perovskites SmBaCo_2-xTi_xO_5+d (x=0.5, 0.7, 1.0, 1.1, 1.3, and 1.5) were analyzed, and their application as electrodes in solid oxide fuel cells (SOFCs) were evaluated. After calcination at 1300℃ for 6 h, a single phase was observed for two compositions of the SmBaCo_2-xTi_xO_5+d oxide system, SmBaCoTiO_5+d (x=1.0) and SmBaCo_0.9Ti_1.1O_5+d (x=1.1). However, the phases of SmBaCoTiO_5+d (SBCTO) and SmTiO₃ coexisted for compositions with x≥1.3 (Ti content). In contrast, for compositions of x≤0.7, the SmBaCo₂O_5+d phase was observed instead of the SmTiO₃ phase. To evaluate the applicability of these materials as SOFC electrodes, the electrical conductivities were measured under various atmospheres (air, N₂, and H₂). SBCTO exhibited stable semi-conductor electrical conductivity behavior in an air and N₂ atmosphere. However, SBCTO showed insulator behavior at temperatures above 600℃ in a H₂ atmosphere. Therefore, SBCTO may only be used as cathode materials. Moreover, SBCTO had an area specific resistance (ASR) value of 0.140 Ω·cm² at 750℃.

• Progress in Superconductivity
• /
• v.4 no.1
• /
• pp.94-98
• /
• 2002

Two kinds of multifilament Bi-2223／Ag tapes, which are different in the precursor calcination temperatures, were heat treated for different time (12, 20, 30, 50, 70, or 100 h) firstly to obtain varied B2223 contents, and then followed by the same pressing and sintering cycles. The relation of the 2223 phase contents after the first sintering and the transport property of the fully processed tapes was studied. The results show that 75-80% 2223 phase formed in tapes before the first cold pressing is beneficial to get a high $I_{c}$ in the final tapes. Compensating the total heat treatment time of the tapes first sintered for 20 h to the same length as that first sintered for 50 h in the subsequent sintering stages, different $I_{c}$ enhancements were observed in these two tapes. No improvement on $I_{c}$ was found in the tape made from the powder calcined at higher temperature, whereas for the tape prepared with the lower temperature calcined powder, the $I_{c}$ was increased to the same level as that first sintered for 50 h. The 2223 contents before the intermediate mechanical work is related to the residual reactants, especially to the liquid phase, which is of vital importance to the phase conversion and healing microcracks, meanwhile, to the size and distribution of the non-superconducting secondary phases. The lower temperature calcined powder resulted in slow formation of 2223 phase, but also provided more reactants and liquid phase for the further phase conversion, as a consequence, for the Improvement of $I_{c}$. c/.

• Nuclear Engineering and Technology
• /
• v.55 no.5
• /
• pp.1519-1526
• /
• 2023

For the first time Aluminium-BariumeZinc oxide nanocomposite (ZABONC) was synthesized by solution combustion method where calcination was carried out at low temperatures (600℃) to study the electromagnetic (EM) (X/γ) radiation shielding properties. Further for characterization purpose standard techniques like PXRD, SEM, UV-VISIBLE, FTIR were used to find phase purity, functional groups, surface morphology, and to do structural analysis and energy band gap determination. The PXRD pattern shows (hkl) planes corresponding to spinel cubic phase of ZnAl₂O4, cubic Ba(NO₃)₂, α and γ phase of Al₂O₃ which clearly confirms the formation of complex nano composite. From SEM histogram mean size of nano particles was calculated and is in the order of 17 nm. Wood and Tauc's relation direct energy band gap calculation gives energy gap of 2.9 eV. In addition, EM (X/γ) shielding properties were measured and compared with the theoretical ones using standard procedures (NaI (Tl) detector and multi channel analyzer MCA). For energy above 356 keV the measured shielding parameters agree well with the theory, while below this value slight deviation is observed, due to the influence of atomic/crystallite size of the ZABONC. Hence synthesized ZABONC can be used as a shielding material in EM (X/γ) radiation shielding.

• Clean Technology
• /
• v.19 no.2
• /
• pp.105-112
• /
• 2013

In this study, polyaniline (PANI)-based $TiO_2$ (PANI-$TiO_2$) composites calcined at different temperatures were prepared and their applications for control of trichloroethylene (TCE) and tetrachloroethylene (TTCE) at indoor air levels were investigated. For these target compounds, the photocatalytic control efficiencies of PANI-$TiO_2$ composites did not exhibit any trend with varying calcination temperatures (CTs). Rather, the average control efficiencies of PANI-$TiO_2$ composites over 3-h photocatalytic process increased from 61 to 72% and from 21 to 39% for TCE and TTCE, respectively, as the CT increased from 350 to $450^{\circ}C$. However, for both the target compounds, the average control efficiencies of PANI-$TiO_2$ composites decreased gradually as the CT increased further to 550 and $650^{\circ}C$. These results were ascribed to contents of anatase crystal phase and specific surface area of different particle sizes in the PANI-$TiO_2$ composites, which were demonstrated by the X-ray diffraction and scanning electron microscopy images, respectively. At the lowest input concentration (IC, 0.1 ppm), average control efficiencies of TCE and TTCE were 72 and 39%, respectively, whereas at the highest IC (1.0 ppm) they were 52 and 18%, respectively. As stream flow rate increased from 0.1 to 1.0 L $min^{-1}$, the average control efficiencies of TCE and TTCE decreased from ca. 100 to 47% and ca. 100 to 18%, respectively. In addition, the average control efficiencies of TCE and TTCE decreased from ca. 100 to 23% and ca. 100 to 8%, respectively as the relative humidity increased from 20 to 95%. Overall, these findings indicated that as-prepared PANI-$TiO_2$ composites could be used efficiently for control of chlorinated compounds at indoor air levels;if operational conditions were optimized.

• Journal of the Korea Institute of Building Construction
• /
• v.20 no.2
• /
• pp.123-128
• /
• 2020

γ-dicalcium silicate(γ-C₂S) is known as a polymorphism of belite. Due to its high CO₂ fixing capacity and the production process with low CO₂ emission, γ-C₂S has attracted more attention of researchers. For the further development of γ-C₂S applications in construction industry, this study aims to investigate the method for synthesizing high purity of γ-C₂S. The influence of raw materials and calcination temperatures on the purity of γ-C₂S was evaluated. Several Ca bearing materials were selected as the calcium source, the materials which's main component is SiO₂ were used as the silicon source. Raw materials were mixed and calcined under different temperatures. The results revealed that the highest purity could be obtained using Ca(OH)₂ and SiO₂ powder as raw materials. In addition, a relatively economic synthesis method using natural mineral materials-limestone and silica sand as raw materials were developed for the practical application. The purity of synthetic γ-C₂S was recorded up to 77.6%.

• Journal of the Korean Magnetics Society
• /
• v.12 no.5
• /
• pp.195-200
• /
• 2002

Low temperature sintering of Co$_2$Z type Ba ferrites with various oxide additives has been studied. Co$_2$Z phase was obtained by 2 step calcination and XRD peaks showed a good agreement with the peaks of the standard Co$_2$Z phase, except for some minor extra peaks. ZnO-B$_2$O$_3$ glass, ZnO-B$_2$O$_3$ and CuO, ZnO-B$_2$O$_3$ and Bi$_2$O$_3$, and ZnO-Bi$_2$O$_3$ glass were added to lower sintering temperatures. Specimens were sintered at the temperature range between 900 $^{\circ}C$ and 1000 $^{\circ}C$. In the single addition of ZnO-B$_2$O$_3$ glass, the specimen with 7.5 wt％ showed the highest shrinkage. Specimens with complex addition of ZnO-B$_2$O$_3$ glass with CuO or Bi$_2$O$_3$ showed higher shrinkages and initial permeabilities than single addition of ZnO-B$_2$O$_3$ glass. Shrinkages and initial permeabilities of the specimens with ZnO-Bi$_2$O$_3$ glass were higher than those of ZnO-B$_2$O$_3$ glass addition.

• Applied Chemistry for Engineering
• /
• v.7 no.5
• /
• pp.1006-1014
• /
• 1996

A series of catalysts, $NiO-ZrO_2/WO_3$, for ethylene dimerization were prepared by coprecipitation from a solution of nickel chloride - zirconium oxychloride mixture followed by dry impregnation with an aqueous solution of ammonium metatungstate and calcination in air. On the basis of the results obtained from x-ray diffraction and DSC, the addition of NiO and $WO_3$ to $ZrO_2$ shifted the transition of $ZrO_2$ from amorphous to a tetragonal phase toward higher temperatures due to the interaction between NiO(or $WO_3$) and $ZrO_2$. $NiO-ZrO_2$ without $WO_3$ was inactive for the ethylene dimerization, but $NiO-ZrO_2/WO_3$ was found to be very active even at room temperature. The high catalytic activity of $NiO-ZrO_2/WO_3$ was closely correlated with the increase of acid strength by the inductive effect of $WO_3$.

• Korean Chemical Engineering Research
• /
• v.40 no.6
• /
• pp.741-745
• /
• 2002

Yttria-stabilized zirconia(YSZ) nanopowders were prepared by sol-gel method using zirconium-n-butoxide(ZNB) and yttrium nitrate as precursors. In addition, the effect of water content added during the hydrolysis reaction of ZNB was investigated on the phase composition and pore structure of the product powders. The phase composition of YSZ nanopowders with calcination temperatures showed the same trend, irrespective of $H_2O$ amounts added during the hydrolysis reaction of ZNB. All powders dried at $100^{\circ}C$ were amorphous and transformed to cubic phase at $400^{\circ}C$, which converted to tetragonal phase at $1,000^{\circ}C$. Monoclinic phase also appeared at $1,000^{\circ}C$. The powders showed the mixture of tetragonal and monoclinic phases from $1,000^{\circ}C$ to $1,400^{\circ}C$. The pore size distributions of the dried powders prepared with small amounts of water(less than or equal to $H_2O/ZNB=20$) showed mesopores, while those prepared with large amounts of water(greater than or equal to $H_2O/ZNB=50$) exhibited micropores.